In the past, the applicant used to develop a kind of "non-sharpening pencil" with insert circulating type pencil lead as showed in FIG. 10, consisting of a hollow tubular body A and a plurality of writing units C having each a pencil lead B installed at its front end and accommodated and held in a head to tail insertion state in the tubular body A. At the time while the pencil lead B installed at the front-most end of writing unit C worn out during writing, the writing unit C positioned at the front end of the tubular body A can be taken off and again inserted into the tubular body A from its rear end in order to extrude the second writing unit C located at the front end of the tubular body A so as to keep on writing continuously. In this way, it is changeable in turn until the last writing unit C worn out finally. Although it has been very good in writing without using any little knife or pencil sharpener, but still there are disadvantages on this kind of writing instrument, such as (1) the whole pencil will be useless if any one of the writing units is lost by accident, (2) it did not meet the requirement of the environmental protection as the whole pencil must be thrown away when every writing units are worn out, (3) the reusable component is the tubular body only and the writing units still need to be thrown away after replaced with new writing units, and it was not comply with the concept of environmental protection as well.
Again referring to FIG. 11, a "non-sharpening pencil" comprises a plurality of socket units E insertible in a head to tail manner forming in series a tubular body D, and a long pencil lead F passing through every socket unit E. The first socket unit E positioned at the front end is detached while the pencil lead F protruding out from the front end of the tubular body is worn out. There is a new pencil lead F extruded out of the socket unit for writing accordingly and the detached socket unit E can be inserted into the receiving hole locating at the rear end of the rear-most socket unit E and thus still maintain the same length of the original tubular body B. Although it was very helpful on reusable purpose of the socket unit, but in case the receiving hole for pencil lead was too loose then it would result in withdrawal of the pencil lead and causing it unable to write at all. When it was too tight then the pencil lead would be broken easily while inserting/coupling the socket units. In addition, the reason why it was not mass-produced and sold in the market was because the used socket units could not have another usage at all.
To solve the above problems in the known writing instruments the inventor had submitted a new writing instrument with detachable function in the art of U.S. Pat. No. 5,044,804 therein not only the serial coupled writing units themselves had no need to be held by an exterior tube any more but also instead that every writing unit could be used as a mini writing instrument individually and also be coupled all together and thus became a long writing instrument as well. Moreover, the used writing units with worn out pencil leads were collectable and then acting as educational building blocks were allowed to be made up into three dimensional toys as one pleases. It was therefore very popular in the markets. However, this kind of writing instrument had little changes in combination and the writing units could only be engaged in same/reverse direction parallel to each other or coupled together one another.
In the light of above facts, the inventor intended to extend the variety of combination and also the additional functions in order to promote the valuation of the relative product and thus came up with an improved building blocks type writing instrument of the present invention.